1. Field of the Invention
This invention relates to an apparatus for drawing circles.
2. Description of the Prior Art
The prior art provides several different types of devices for drawing circles. Most of these devices require a sharp and usually metal point such as a compass tip to act as a pivot to which a pivot arm is connected having a means for marking such as a pencil lead attached to an opposite end of the pivot arm for inscribing a circle. Devices which employ a sharp pointed member may be unsuitable for use by children due to their inherent dangerousness.
Additionally, the sharp point defaces the paper or other surface on which the circles being inscribed by putting a small hole in the surface.
There are other devices in the prior art for drawing circles which do not incorporate any sharp points which are usually sheets of plastic material having various sized holes therein which are lined concentrically with the point about which the circle is to be drawn in the pencil or other writing instrument is abutted against the circumferential wall of the hole and is guided along that wall so as to inscribe a circle on the surface under the plastic sheet. This type of device requires a sheet which is greater in diameter than the circle which is to be drawn, and additionally, if several holes are incorporated in the same sheet, the size of the sheet increases by greater than the diameter of each additional hole.
My prior patent, U.S. Pat. No. 4,353,166 discloses a circle drawing instrument which is compact in form and has no sharp points. The device is comprised of a disk rotatably carried on a sheet adjacent and concentric to a hole in the sheet. The disk and sheet each have a series of holes therein spaced from a center point of the disk into which the tip of a suitable writing instrument may be placed to rotate the disk or sheet with respect to the other, thus inscribing a circle on a desired surface.
In my prior device, the series of holes spaced from the center of the disk which define the radius of the circle to be inscribed are fixed with respect to the center point of the disk and thus only those circles whose radius is defined by one of the predefined holes can be inscribed by this instrument.